3 solar controllers to one battery bank?

[Tim Good]

I have two solar controllers into my 4 Trojan battery bank. I had a MPPT victron connected to 360w of panels and then I added another 60w panel on the coach roof on a long cable which could roam around deck. As such I a standard controller on for this one.

My current two controllers work fine side by side and don’t appear to force one or the other into float.

I now want to add another array somewhere else. Has anyone else use 3 or more controllers into one bank successfully?

 

[RichardS]

Can you not connect the new bank to the existing Victron? You will get the most out of the panels if one MPPT is doing all the processing, provided it's not overloaded,

Richard

 

[Tim Good]

Can you not connect the new bank to the existing Victron? You will get the most out of the panels if one MPPT is doing all the processing, provided it's not overloaded,

Richard

My controller isn’t big enough to take more. But assuming I upgraded to a new bigger controller then I don’t think I could feed in one bank of 450w (3x120w in series) and then another bank of different overall power somewhere else? Unless I’m mistaken?

 

[rogerthebodger]

I have 4 solar controllers feeding my domestic bank and a single controller feeding my engine bank.

My domestic has 2 on/off controllers and 2 PWM controllers and all work fine together.

My engine solar controller can also be switched to feed my domestic bank so I could have 5 controllers feeding my domestic bank with no problem.

What I do find is that as the voltage of my domestic bank rises the controllers switch off or start to reduce the feed as a single controller would.

I have also set it up so when I leave the boat for some time I can switch out the 2 PWM controllers so the smaller controllers just trickle charge the domestic banks.

 

[RichardS]

My controller isn’t big enough to take more. But assuming I upgraded to a new bigger controller then I don’t think I could feed in one bank of 450w (3x120w in series) and then another bank of different overall power somewhere else? Unless I’m mistaken?

As long as the controller is able to handle the maximum voltage and the maximum current, which you can calculate from the panel specs, then they can all be connected into the same MPPT controller and the controller will get the best out of the array, including reaching the threshold voltage as early as possible.

Richard

 

[PaulRainbow]

My controller isn’t big enough to take more. But assuming I upgraded to a new bigger controller then I don’t think I could feed in one bank of 450w (3x120w in series) and then another bank of different overall power somewhere else? Unless I’m mistaken?

The voltage needs to be the same, wattage doesn't matter. So you could connect 3x120w in series, 3x50w in series and connect the two "banks" in parallel. You cannot mix voltages though, so you couldn't parallel a pair of series wired 50w panels to the 3x120w panels.

You could also connect, in series, a fourth panel to the existing bank of three, but be aware that shading any one panel has a bad effect on all of the panels in series.

 

[noelex]

Three solar controllers is generally fine. If they are MPPT controllers there is a significant advantage of this approach because the maximum power point can be different for each of the controllers. This helps extract the best power from the solar panels, especially on a yacht.

The only drawback is a slightly higher self consumption and the risk of some conflict with the charging algorithm. The latter problem is minimised if controllers with fine and multiple user adjustable set points are selected.

 

[geem]

We have just swapped from using two Victron 75/15 blue solar controllers to a single 100/30 smart solar with smart sense battery voltage module. We run two series pairs of 180w panels giving us 720w of solar into our domestic bank. The charging of the batteries is now far more consistent and reliable. Previously we would have one 75/15 in bulk and one in float! They both had the same settings but since one set of panels would be in shade in the morning it would start off its charge cycle with a different set point voltage so would run a different charge cycle to the other regulator. Not the best use of the solar panels and not the best charge regime for the batteries. In addition I found the Victron Blue solar regs did not give accurate battery temperature as they have no battery temperature compensation. The smart sense does have this feature. We are running a smart solar 75/10 for the engine batteries and its interesting to note that the two banks of batteries are usually 2degC different. This is because at anchor the domestic bank needs charge whilst the engine batteries don't once they are charged up. If you have Blue solar regs and they are not in the battery compartment and your battery box is not very well ventilated with mechanical ventilation then it is possible you are over charging your batteries. I believe this was my scenario until I install good ventilation and changed to proper battery temperature sensed charge regulators

 

[noelex]

The charging of the batteries is now far more consistent and reliable. Previously we would have one 75/15 in bulk and one in float!

This can be a problem, but it can usually be fixed on most regulators by adjusting the settings. It was particularly a problem with the Victron controllers prior to the release of the 1:42 firmware. The tail amp setting would prematurely drop the controller into float. The 1:42 firmware allows this setting to be disabled if you go into advanced mode. This needs to be done if you have more than one controller.

Overall, multiple controllers (ideally one per panel) will result in more output than series or parallel connection to a single controller, but the controller software and the adjustment of settings is quite critical. The default values often do not work.

 

[geem]

This can be a problem, but it can usually be fixed on most regulators by adjusting the settings. It was particularly a problem with the Victron controllers prior to the release of the 1:42 firmware. The tail amp setting would prematurely drop the controller into float. The 1:42 firmware allows this setting to be disabled if you go into advanced mode. This needs to be done if you have more than one controller.

Overall, multiple controllers (ideally one per panel) will result in more output than series or parallel connection to a single controller, but the controller software and the adjustment of settings is quite critical. The default values often do not work.

I tried using the latest firmware but still could not resolve the situation where one reg was in float and the other in bulk. For example, if they were both in float then you turned on a large load they would both go to bulk. One reg would soon get back to float as it had full sun. The other would have partial sun and would not perform the same. Once the panels in full sun went in to absorption, then float their voltage input would drop. The second panel would have some shading but still manage to get the volts up close to their absorption voltage but not enough to get them to trip in to absorption. As a result the batteries would sit at an elevated voltage for some hours. With the single controller this problem has gone away.

 

[noelex]

The settings on these controllers are complex and this is not covered well in any of the literature from the manufacturer.

Did you disable the “tail amp” setting? To do this you need to go into “expert mode” and ignore all the warnings .

The tail amp setting can be useful in some situations, but it can, and often does, stop the controller playing nicely with other solar controllers. A premature and inappropriate drop to float by one of the controllers is the usual symptom so I suspect this was the problem in your case.

If you disable the tail amp setting it solves 90% of these conflict issues although there are some other settings that can be important. With the right settings multiple Victron controllers can work well together and provide the advantage of individual tracking for each solar panel which gives a slightly higher yield.

 

[geem]

The settings on these controllers are complex and this is not covered well in any of the literature from the manufacturer.

Did you disable the “tail amp” setting? To do this you need to go into “expert mode” and ignore all the warnings .

The tail amp setting can be useful in some situations, but it can, and often does, stop the controller playing nicely with other solar controllers. A premature and inappropriate drop to float by one of the controllers is the usual symptom so I suspect this was the problem in your case.

If you disable the tail amp setting it solves 90% of these conflict issues although there are some other settings that can be important. With the right settings multiple Victron controllers can work well together and provide the advantage of individual tracking for each solar panel which gives a slightly higher yield.

The tail voltage was disabled. I posted on the Victron forum but didnt get a solution. Happy now with current solution

 

[Allan]

Can anyone quantify how much energy is lost (ie not going into the battery) when one regulator is in the wrong mode? I've often wondered if using wind and solar has the same problem. (Rutland 913 with Marlec HRDi and 3 x 50w panels in series with Victron 75/15)
Allan

 

[lw395]

Can anyone quantify how much energy is lost (ie not going into the battery) when one regulator is in the wrong mode? I've often wondered if using wind and solar has the same problem. (Rutland 913 with Marlec HRDi and 3 x 50w panels in series with Victron 75/15)
Allan

If your solar controller wakes up to find the battery at 13+ volts because it's being charged by another source, it will probably estimate that the battery doesn't need much charge and reduce the absorption time to the minimum.

But every installation is a little different, and every day is different. Plus there are dozens of diferent releases of firmware in some of these controllers.

Your best bet is to observe what actually happens on your boat.

 

[noelex]

The tail voltage was disabled. I posted on the Victron forum but didnt get a solution. Happy now with current solution

Interesting that you still had the problem with the tail amp setting off. It would have been nice to find out why the conflict was occurring. Anyway, it sounds like you have solved the problem with one controller.

 

[noelex]

Can anyone quantify how much energy is lost (ie not going into the battery) when one regulator is in the wrong mode? I've often wondered if using wind and solar has the same problem. (Rutland 913 with Marlec HRDi and 3 x 50w panels in series with Victron 75/15)
Allan

Yes, the same problem can occur whenever there are two charge sources of any type. Conflicts do not often cause much loss, but any loss of potential power is annoying and should not occur. As well as undercharging, multiple charge sources can also overcharge and damage the battery. However, it is important to understand that when multiple charge sources are behaving differently (for example one solar controller is putting out a lot of current while the other controller is putting out very little) this is not necessarily a sign that there is a problem. Multiple charge sources will never have exactly the same set points so it is not unusual for one source to predominant. Providing the battery is continually correctly charged at the appropriate voltage, this is not a problem.

The sign that there is a problem is if the battery should be at a higher voltage and one charge source is capable of delivering more current, but is not doing so.

An anology may help. Imagine a hybrid car with both petrol and electric engines. If the car is traveling at the desired speed but all of the power is suplied by the electric motor, this does not indicate a problem. There is no need for the power to be shared between the petrol and electric engines.

However, if the driver pushes down on the accelerator to overtake and the electric engine cannot deliver the desired acceleration, the petrol engine should kick in and deliver the required extra power. Of course not all hybrid cars are designed to perform this way, but I think the analogy helps.

 

[noelex]

If your solar controller wakes up to find the battery at 13+ volts because it's being charged by another source, it will probably estimate that the battery doesn't need much charge and reduce the absorption time to the minimum.

This depends on the charge controller. Very few models behave this way. Most have a fixed absorption time.

The popular Victron controllers are an exception. They do have a variable absorption time based on the voltage at wake up, however, this can be disabled (in the expert mode) and converted to a fixed absorption time.

The variable absorption time will not necessarily cause a conflict and I would not change to fixed absorption time unless there is an issue, but it is an option that can sometimes be helpful. The default values rarely work optimally especially with multiple charge sources so it is worth buying a controller with viable parameters and different options so the charge profile can be adequately adjusted.

 

[lw395]

Fundamentally, any 'smart' battery charging controller has to make decisions about the state of charge of the battery.
There are many ways of doing that, most of which are hard to do if the battery is being charged (or even discharged) by a circuit which the controller knows nothing about.
It doesn't help if the people tasked with designing the controller were not asked to design something used alongside other chargers.

Obviously it's not too much of a worry if you don't need any 'smart' behaviour and just want to whack in all the power you can get, because there's rarely enough sun to worry about in England.
Or if you're prepared to monitor and intervene manually every day.
If you are actually going to rely on your controller being 'smart' to look after your batteries properly, long term, you need to understand the detail of how each controller will make decisions about the state of charge of the battery.
Or just let one controller work as its designers were asked to make it work.

 

[geem]

Fundamentally, any 'smart' battery charging controller has to make decisions about the state of charge of the battery.
There are many ways of doing that, most of which are hard to do if the battery is being charged (or even discharged) by a circuit which the controller knows nothing about.
It doesn't help if the people tasked with designing the controller were not asked to design something used alongside other chargers.

Obviously it's not too much of a worry if you don't need any 'smart' behaviour and just want to whack in all the power you can get, because there's rarely enough sun to worry about in England.
Or if you're prepared to monitor and intervene manually every day.
If you are actually going to rely on your controller being 'smart' to look after your batteries properly, long term, you need to understand the detail of how each controller will make decisions about the state of charge of the battery.
Or just let one controller work as its designers were asked to make it work.

I agree but two observation from my own experience is that if you run several different solar panels with their own controllers then it really doesn't matter so much whats going on. The individual charge amps are all relatively small. If one charger controller is in float and others are bulk charging then the loss to your charging regime is small. If most charge regs are in float and one stays in bulk then this is unlikely to have an impact on your battery life. Where is became a problem for me was having two large solar arrays at 360w each. As explained in a previous post. I witnessed over charging and under utilisation of the solar array. One large regulator for all my domestic solar has cured the problem.

 

[noelex]

Fundamentally, any 'smart' battery charging controller has to make decisions about the state of charge of the battery.
There are many ways of doing that, most of which are hard to do if the battery is being charged (or even discharged) by a circuit which the controller knows nothing about.
It doesn't help if the people tasked with designing the controller were not asked to design something used alongside other chargers.

Obviously it's not too much of a worry if you don't need any 'smart' behaviour and just want to whack in all the power you can get, because there's rarely enough sun to worry about in England.
Or if you're prepared to monitor and intervene manually every day.
If you are actually going to rely on your controller being 'smart' to look after your batteries properly, long term, you need to understand the detail of how each controller will make decisions about the state of charge of the battery.
Or just let one controller work as its designers were asked to make it work.

Most (not all) solar controllers actually don’t make any attempt to determine the battery state of charge. They go through the same regime irrespective of state of charge. However, the battery itself will influence the voltage points. So the charge rate and total charge amount varies even though the formula used by the solar controller stays the same.

An example of a typical solar controllers algorithm would be:

Raise the battery voltage until it reaches 14.7v then hold this voltage at this level for two hours (counting only the time when the voltage is at 14.7v) and then drop to 13.8v. A new cycle is started every day or if the battery voltage drops below 12.4v.

This formula from the solar controller stays exactly the same. The controller makes no attempt to judge if the battery is very flat or full.

However, a flat battery will take a long time before the voltage reaches 14.7v and a full battery will reach reach this voltage very quickly. A flat battery will also frequently drop below 14.7v so the absorption timer will stop. So the energy delivered by the solar controller will be much more into the flat battery even though the formula stays the same. Thus a controller that makes no attempt to judge the battery state of charge can do a reasonable job of correctly charging batteries at various state of charge.

There are variations on the above. Notably the Victron controllers if left at their default values will adjust the absorption time (two hours in the above example) based on the voltage in the morning. They will also terminate the absorption phase if the output current drops below a certain level (this is different for the different models, but typically around 1A). However, the Victron controllers are very unusual. The algorithm they used prior to the 1:42 firmware update was very different to most other solar controllers. The new firmware has brought the Victron models more into line with models from other manufacturers, but at the default values they still do things a little differently.

Basically, the controllers are not very smart despite the label. Some manufacturers have optional equipment to make them smarter. If the current entering the battery is comunicated to the controller the termination of the absorption phase can be more accurate, but very few boats have these options installed.